This invention relates to a circuit for controlling a current source transistor.
A large number of circuits are known for the production of temperature-compensated transistor currents. The temperature is compensated for example, by applying bias voltages at the base-emitter paths of the transistors, through which constant currents have flowed, at diode paths operated in the direction of flow, these diode paths having the same temperature characteristics as the transistors.
However it is not absolutely certain from this temperature compensation that the currents flowing through the transistors are independent of the magnitude of the d.c. supply voltage. This is because the current sources do not have an infinitely large resistance and moreover, as the collector-emitter voltages across the transistors increase, which may be caused for example by the increase in the d.c. supply voltage, the collector current through these transistors rises because of the current voltage characteristics which are specific to the component. In a push-pull output stage, this means, for example, that the collector quiescent current also rises through the output stage transistors as operating voltage rises even if this collector quiescent current is produced with the aid of a temperature-stabilising circuit. This undesirble increase in the quiescent collector current through output stage transistors of the push-pull output stage may lead to self-destruction of the output stage transistors as the operating voltage rises.